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Spin Structure with JLab 6 and 12 GeV J. P. Chen, Jefferson Lab INT-12-49W: Workshop on Orbital Angular Momentum in QCD, Feb. 6, 2011 Overview Selected Results from JLab 6 GeV A 1 at High-x: Valence Quark Spin Distributions Moments g 2 /d 2 : B-C Sum Rule, Color Lorentz Force (Polarizability) SIDIS: Transversity and Flavor Decomposition Planned experiments with JLab 12 GeV

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Introduction Spin experiments provide fundamental information as well as insights into QCD dynamics Experiments: polarized beams(e, p), polarized targets (p, d, 3 He/n) longitudinal and transverse target polarization A||, A|_ A 1, A 2 ||, |_ Spin Structure Functions g 1 (x, Q 2 ), g 2 (x, Q 2 ) Role of unpolarized PDFs/ R Polarized PDFs q(x) LO, NLO,…, QCD evolution, Higher-twists Moments, sum rules High-x, low-x World data (CERN, SLAC, HERMES, RHIC-spin, JLab, …) JLab 6 GeV: high-x, low Q 2, high-precision., Future :12 GeV

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Jefferson Lab Experimental Halls HallA: two HRS’ Hall B:CLAS Hall C: HMS+SOS 6 GeV polarized CW electron beam Pol=85%, 200 A Will be upgraded to 12 GeV by ~2014

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JLab Polarized Proton/Deuteron Target Polarized NH 3 /ND 3 targets Dynamical Nuclear Polarization In-beam average polarization 70-90% for p 30-50% for d Luminosity ~ (Hall C/A) ~ (Hall B)

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JLab Polarized 3 He Target longitudinal, transverse and vertical Luminosity=10 36 (1/s) (highest in the world) Record high pol ~ 60% 60% 15 uA

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6 GeV JLab 12 CHL-2 Upgrade magnets and power supplies Enhance equipment in existing halls add Hall D (and beam line)

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Experimental Halls (new) Hall D: linear polarized photon beam, Selonoid detetcor GluoX collaboration: exotic meson spectroscopy gluon-quark hybrid, confinement Hall B: CLAS12 GPDs, TMDs, … Hall C: Super HMS + existing HMS Form factors, structure functions (A1n/d2n), … Hall A: Dedicated devices + existing spectrometers Super BigBite, SoLID, MOLLER SIDIS (transversity/TMDs), PVDIS, …

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JLab Spin Experiments Results: Published and Preliminary/Upcoming Spin in the valence (high-x) region Spin (g 1 /g 2 ) Moments: Spin Sum Rules, d 2 SSA in SIDIS: Transversity (n) SSA in Inclusive Reaction On-going g 2 p at low Q 2 Future: 12 GeV Inclusive: A 1 /d 2, Semi-Inclusive: Transversity, Flavor-decomposition Reviews: S. Kuhn, J. P. Chen, E. Leader, Prog. Part. Nucl. Phys. 63, 1 (2009)

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Valence Quark Spin Structure A 1 at high x and flavor decomposition

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Why Are PDFs at High x Important? Valence quark dominance: simpler picture -- direct comparison with nucleon structure models SU(6) symmetry, broken SU(6), diquark x 1 region amenable to pQCD analysis -- hadron helicity conservation? role of quark orbit angular momentum? Clean connection with QCD, via lattice moments (d 2 ) Input for search for new physics at high energy collider -- evolution: high x at low Q 2 low x at high Q 2 -- small uncertainties amplified -- example: HERA ‘anomaly’ (1998)

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World data for A 1 Proton Neutron

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JLab E Precision Measurement of A 1 n at Large x Spokespersons: J. P. Chen, Z. Meziani, P. Souder; PhD Student: X. Zheng First precision A 1 n data at high x Extracting valence quark spin distributions Test our fundamental understanding of valence quark picture SU(6) symmetry Valence quark models pQCD (with HHC) predictions Quark orbital angular momentum Crucial input for pQCD fit to PDF PRL 92, (2004) PRC 70, (2004)

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Polarized Quark Distributions Combining A 1 n and A 1 p results Valence quark dominating at high x u quark spin as expected d quark spin stays negative! Disagree with pQCD model calculations assuming HHC (hadron helicity conservation) Quark orbital angular momentum Consistent with valence quark models and pQCD PDF fits without HHC constraint

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Inclusive Hall A and B and Semi-Inclusive Hermes BBS BBS+OAM H. Avakian, S. Brodsky, A. Deur, and F. Yuan, PRL 99, (2007) pQCD with Quark Orbital Angular Momentum

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Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon Preliminary A 1 (p) Results, Hall C SANE Courteous of O. Rondon

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Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky Preliminary A 1 ( 3 He) Results, Hall A E Courteous of D. Flay

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Spin-Structure in Resonance Region: E Spokesperson: N. Liyanage, J. P. Chen, S. Choi; PhD Student: P. Solvignon PRL 101, (2008) A 1 3He (resonance vs DIS) 1 resonance vs. pdfs xQ2Q2 x

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A 1 p at 11 GeV (CLAS12) Projections for JLab at 11 GeV A 1 n at 11 GeV (Hall C/A)

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u and d at JLab 11 GeV Polarized Sea GeV

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multiplicities in SIDIS ep→e’ X DSS (Q 2 =2.5GeV 2 ) DSS (Q 2 =25GeV 2 ) CLAS 6 Hall-C

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Moments of Spin Structure Functions Sum Rules, Polarizabilities

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First Moment of g 1 p : 1 p EG1b, arXiv: EG1a, PRL 91, (2003) Spokespersons: V. Burkert, D. Crabb, G. Dodge, 1p1p Total Quark Contribution to Proton Spin (at high Q 2 ) Twist expansion at intermediate Q 2, LQCD, ChPT at low Q 2

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First Moment of g 1 n : 1 n E94-010, PRL 92 (2004) E97-110, preliminary EG1a, from d-p 1n1n

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1 of p-n EG1b, PRD 78, (2008) E EG1a: PRL 93 (2004)

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Second Spin Structure Function g 2 Burkhardt - Cottingham Sum Rule d 2 : Color Lorentz Force (Polarizability) Spin Polarizabilities

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Precision Measurement of g 2 n (x,Q 2 ): Search for Higher Twist Effects Measure higher twist quark-gluon correlations. Hall A Collaboration, K. Kramer et al., PRL 95, (2005)

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BC Sum Rule P N 3 He BC = Meas+low_x+Elastic 0

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BC Sum Rule P N 3 He BC satisfied w/in errors for 3 He BC satisfied w/in errors for Neutron (But just barely in vicinity of Q 2 =1!) BC satisfied w/in errors for JLab Proton 2.8 violation seen in SLAC data very prelim

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Color Lorentz Force (Polarizability): d 2 2 nd moment of g 2 -g 2 WW d 2 : twist-3 matrix element d 2 and g 2 -g 2 WW : clean access of higher twist (twist-3) effect: q-g correlations Color polarizabilities are linear combination of d 2 and f 2 Provide a benchmark test of Lattice QCD at high Q 2 Avoid issue of low-x extrapolation Relation to Sivers and other TMDs

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d 2 (Q 2 ) E “g2p” SANE “d2n” new in Hall A 6 GeV Experiments Sane: new in Hall C “g2p” in Hall A, 2011 projected

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Preliminary results on neutron from E Spokespersons: J. P. Chen, S. Choi, N. Liyanage, plots by P. Solvignon

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Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon Preliminary A 2 (p) Results, Hall C SANE Courteous of O. Rondon

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Projection on d2p from Hall C SANE

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Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky Projection on Hall A E (d 2 n ) Courteous of D. Flay

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E : Proton g 2 Structure Function Fundamental spin observable has never been measured at low or moderate Q 2 BC Sum Rule : violation suggested for proton at large Q 2, but found satisfied for the neutron & 3 He. Spin Polarizability : Major failure (>8 of PT for neutron LT. Need g 2 isospin separation to solve. Hydrogen HyperFine Splitting : Lack of knowledge of g 2 at low Q 2 is one of the leading uncertainties. Proton Charge Radius : also one of the leading uncertainties in extraction of from H Lamb shift. BC Sum Rule Spokespersons: A. Camsonne, J. P. Chen, D. Crabb, K. Slifer, 6 PhD students Scheduled to run 2/2012-5/2012 Spin Polarizability LT

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Spin Polarizabilities Preliminary E (and Published E94-010) Spokesperson: J. P. Chen, A. Deur, F. Garibaldi, plots by V. Sulkosky Significant disagreement between data and both ChPT calculations for LT Good agreement with MAID model predictions 0 LT Q2 Q2 Q2 Q2

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Single Target-Spin Asymmetries in SIDIS Transversity/Tensor Charge

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Transversity Three twist-2 quark distributions: Momentum distributions: q(x,Q 2 ) = q ↑ (x) + q ↓ (x) Longitudinal spin distributions: Δq(x,Q 2 ) = q ↑ (x) - q ↓ (x) Transversity distributions: δq(x,Q 2 ) = q ┴ (x) - q ┬ (x) It takes two chiral-odd objects to measure transversity Semi-inclusive DIS Chiral-odd distributions function (transversity) Chiral-odd fragmentation function (Collins function)

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E He Target Single-Spin Asymmetry in SIDIS Spokespersons: J. P. Chen, E. Cisbani, H. Gao, X. Jiang, J-C. Peng, 7 PhD students 3 He Sivers SSA: negative for π +, 3 He Collins SSA small Non-zero at highest x for + Blue band: model (fitting) uncertainties Red band: other systematic uncertainties X. Qian, et al. PRL (2011)

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Results on Neutron Collins asymmetries are not large, except at x=0.34 Sivers negative Blue band: model (fitting) uncertainties Red band: other systematic uncertainties

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12 GeV: Mapping of Collins Asymmetries with SoLID Both + and - For one z bin ( ) Will obtain many z bins ( ) Tensor charge E He(n), Spokespersons: J. P. Chen, H. Gao, X. Jiang, J-C. Peng, X. Qian E (p), Spokespersons: K. Allda, J. P. Chen, H. Gao, X. Li, Z-E. Mezinai

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Summary Spin structure study full of surprises and puzzles A decade of experiments from JLab: exciting results valence spin structure precision measurements of g 2 /d 2 : high-twist spin sum rules and polarizabilities first neutron transversity Bright future 12 GeV Upgrade will greatly enhance our capability Precision determination of the valence quark spin structure flavor separation Precision measurements of g 2 /d 2 Precision extraction of transversity/tensor charge

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